Microbial mats are laminated benthic ecosystems made up of microorganisms having diversely coloured layers due to the photosynthetic pigments of cyanobacteria, algae and purple anoxygenic phototrophic bacteria. For many years, our group of work has been studying the microbial mats in the Ebro Delta (Tarragona, Spain). Despite the fact that the Ebro Delta has been a protected area for years, is currently subjected to anthropogenic pollution. Heavy metal contamination in these environments is very considerable, making the microorganisms in these ecosystems a subject of great interest when analyzing their ability to sequester metals. Our group has optimized different high-resolution microscopy techniques such as Confocal Laser Scanning Microscopy (CLSM), Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM), these last two techniques coupled to an Energy dispersive X-ray detector (EDX). The CLSM coupled to a spectrofluorometric detector (CLSM-λscan) was applied in determining the in vivo effect of lead (Pb) in phototrophic microorganisms (tolerance/resistance), and the CLSM and image analysis (CLSM-IA) were used in determining changes in total and individual cyanobacteria biomass. Additionally, the electron microscopic techniques were utilized in determining the ability of these microorganisms to capture metal both externally in extrapolymeric substances (EPS) and internally, in polyphosphate inclusions (PP). For this purpose, we used different cyanobacteria from Pasteur culture collection (Oscillatoria sp. PCC 7515, Chroococcus sp. PCC 9106 and Spirulina sp. PCC 6313) and Microcoleus sp. isolated from Ebro Delta microbial mats. Pb was selected because the Ebro River is polluted by this metal and also because it is a non-essential toxic metal. An inverse correlation between the mean fluorescence intensity (MFI) and the concentration of the metal used have been demonstrated in all phototrophic bacteria tested in CLSM-λscan. On the other hand, the SEM-EDX and TEM-EDX analysis showed that all phototrophic microorganisms have the ability to accumulate Pb in EPS and in PP inclusions. Experiments made in unpolluted and polluted microcosms, demonstrated that cyanobacteria from the polluted microcosm accumulate Pb in PP inclusions, whilst no Pb was detected in the unpolluted microcosm by means of TEM-EDX. Finally, the TEM-EDX analyses spectra from PP inclusions of different cyanobacteria from Ebro Delta microbial mats samples, demonstrated that no type of metal pollution was detected. It can be deduced that this ecosystem was pristine during the sampling procedure. In conclusion, the combination of the techniques outlined here provides valuable information to select cyanobacteria as bioindicators of metal pollution and its potential for bioremediation. © 2013 by Nova Science Publishers, Inc. All rights reserved.
|Title of host publication||Cyanobacteria: Ecology, Toxicology and Management|
|Number of pages||16|
|Publication status||Published - 1 May 2013|